1. Field of the Invention
The present invention provides a communications system and method. Specifically, a system and a method is disclosed that provides SDMA (spatial division multiple access) communication channels in a non-SDMA system. The present invention utilizes a smart antenna that takes advantage of the same communication channel to emit a plurality of spatial spectrums. The spatial spectrums are used to transmit information and establish wireless communications with a plurality of mobile stations at different positions. The present invention uses the limited numbers of communication channels efficiently without lowering the communication quality.
2. Description of Prior Art
Please refer to FIG. 1. FIG. 1 is a schematic diagram of a prior art wireless communications system 10. The wireless communications system 10 is located in a communications area 12, which is one of a plurality of such communications areas (not shown). The system 10 effects wireless communications with mobile stations, such as a mobile phone 14. The wireless communications system 10 includes an omnidirectional antenna 16 that emits wireless signals in every direction, a base transceiver station (BTS) 18, and a base station controller (BSC) 20. The base station controller 20 controls the transmitting and receiving of information between the mobile phone 14 in the specific communications area 12 and other communications networks. The base transceiver station 18 is connected with the base station controller 20 and effects the wireless communications between one or many mobile phones and the base station controller 20. Because the omnidirectional antenna 16 emits wireless signals in every direction, that is the signals are non-directional, many mobile phones must use different wireless communication channels to prevent interference between them if they try to simultaneously establish wireless communications with the base station controller 20. But the number of wireless communication channels is limited in the wireless communications system 10, especially in a multi-user communications system, and so increasing the number of users or providing a higher quality of communications service cannot be done because of interference conditions. For example, if the wireless communications system 10 is designed to use thirty sets of predetermined communication channels in the communications area 12, it can establish wireless communications with at most thirty users. Other communications areas near the communications area 12 must not use these thirty sets of communication channels to prevent interference. So, the reuse efficiency of the communication channels is limited and cannot be improved.
Please refer to FIG. 2. FIG. 2 is a schematic diagram of another prior art wireless communications system 30. The wireless communications system 30 includes a group of antennas or a plurality of antennas 32, 34, and 36, a plurality of corresponding base transceiver stations 52, 54, and 56, and a base station controller 60. Wireless communications for a communications area 28 is effected by the wireless communications system 30, and is partitioned into different communications sectors 22, 24, and 26 in advance. Antennas corresponding to each communications sector are responsible for transmitting and receiving wireless information transmitted to the base station controller 60 by the corresponding base transceiver stations. For example, every base transceiver station has ten sets of communication channels if the communications area 28 is designed to use thirty predetermined sets of communication channels. As discussed above, the base transceiver station 52 can support the wireless communications of ten mobile phones in its territory, as can the base transceiver stations 54 and 56. Hence, thirty mobile phones are available at the same time, and the reuse efficiency of the wireless communications system 30 is better than that of the wireless communications system 10. But the wireless communications system 30 has to set up more base transceiver stations like 52, 54, and 56, and so the overall cost of the system 30 is increased. Furthermore, because wireless communications between different users is achieved by using different communication channels, the reuse efficiency of the wireless communication channels cannot fulfill more and more communications demands.
An SDMA (spatial division multiple access) wireless communications system including a smart antenna, one or a plurality of base transceiver stations, and a base station controller, has been proposed to solve the problems discussed above. The smart antenna is used to transmit and receive directional wireless signals, and establishes wireless communications with users in a specific area. The base transceiver station and the base station controller include software and hardware equipment for SDMA. Because the SDMA wireless communications system can handle directional wireless signals from mobile phones and recognize their position, its reuse efficiency of communication channels is greatly improved. U.S. Pat. No. 5,886,988 has also proposed a method for improving the software procedure in the base transceiver station and improving the communications quality. Not every wireless communications system is SDMA, however, and it costs a lot to change the original system to an SDMA system.
The present invention provides SDMA communication channels for a non-SDMA wireless communications system. When a plurality of mobile stations in different positions try to establish wireless communications, the mobile stations also use the same communication channels with different direction information for recognizing and achieving the goal of high reusability for the original communication channels, with a lower cost.